This invention relates to asphalt-based roofing materials, and in particular to depositing protective and decorative shingle granules onto an asphalt coated sheet, for such uses as asphalt strip shingles.
Asphalt-based roofing materials, such as roofing shingles, roll roofing and commercial roofing, are installed on the roofs of buildings to provide protection from the elements, and to give the roof an aesthetically pleasing look. Typically, the roofing material is constructed of a substrate such as a glass fiber mat or an organic felt, an asphalt coating on the substrate, and a surface layer of granules embedded in the asphalt coating.
A common method for the manufacture of asphalt shingles is the production of a continuous sheet of asphalt material followed by a shingle cutting operation which cuts the material into individual shingles. In the production of asphalt sheet material, either a glass fiber mat or an organic felt mat is passed through a coater containing hot liquid asphalt to form a tacky, asphalt coated sheet. Subsequently, the hot asphalt coated sheet is passed beneath one or more granule applicators which discharge protective and decorative surface granules onto portions of the asphalt sheet material.
In the manufacture of colored shingles, two types of granules are typically employed. Headlap granules are granules of relatively low cost used for the portion of the shingle which will be covered up on the roof. Colored granules or prime granules are of relatively higher cost and are applied to the portion of the shingle that will be exposed on the roof.
To provide a color pattern of pleasing appearance, the colored portion of the shingles may be provided with areas of different colors. Usually the shingles have a background color and a series of granule deposits of different colors or different shades of the background color. A common method for manufacturing the shingles is to discharge blend drops onto spaced areas of the tacky, asphalt coated sheet. Background granules are then discharged onto the sheet and adhere to the tacky, asphalt coated areas of the sheet between the granule deposits formed by the blend drops. The term xe2x80x9cblend dropxe2x80x9d, as used herein, refers to the flow of granules of different colors or different shades of color (with respect to the background color) that is discharged from a granule blend drop applicator onto the asphalt coated sheet. The patch or assemblage of the blend drop granules on the asphalt coated sheet is also referred to as the xe2x80x9cblend dropxe2x80x9d.
One of the problems with conventional granule application equipment is that it depends on mechanical movement to discharge blend drops onto the moving asphalt coated sheet. Usually the granules are fed from a hopper by means of a fluted roll from which, upon rotation, the granules are discharged onto the sheet. The roll is ordinarily driven by a drive motor, and the roll is positioned in the drive or non-drive position by means of a brake-clutch mechanism. The requirement for mechanical action has inherent limitations which prevent a very precise beginning and ending to the blend drop. Also, once the mechanical action takes place, there is a short time lag as the inertia of the granules is overcome. Consequently, there is a limit to the sharpness of the blend drops on the shingle. As shingle manufacturing lines go up in speed, the lack of sharpness is accentuated and the distinction between the blend drop granule deposits, and the background color becomes fuzzy. The lack of sharpness puts a severe limitation on the kinds of patterns and color contrasts that can be applied to shingles at high production speeds.
A known granule depositing method designed to overcome the sharpness problem of conventional granule applicators is shown in U.S. Pat. No. 5,795,389 issued to Koschitzky, which is hereby incorporated by reference in its entirety. The Koschitzky reference discloses an auxiliary belt onto which a series of patches of granules is deposited. The auxiliary belt is positioned above the asphalt coated sheet, and includes an upper flight and a lower flight, with the upper flight travelling in a direction opposite that of the asphalt coated sheet. At the upstream end of the auxiliary belt (i.e., upstream with respect to the movement of the asphalt coated sheet) the upper flight of the auxiliary belt turns around a belt roller to form the lower flight. A retaining conveyor is wrapped around the upstream end of the auxiliary conveyor to keep the granules from flying about as the granules are turned into a downward direction. The granules of each of the patches are dropped vertically straight down onto the asphalt coated sheet to form blend drops. After the blend drops are applied to the asphalt coated sheet the background granules are applied to form a granule coated sheet, which is then cooled and cut into individual granule coated shingles. The Koschitzky patent also discloses that a shroud, instead of a retaining conveyor, can be used to direct the granules into a downwardly directed vertical stream of granules.
While the retaining conveyor disclosed in the Koschitzky patent is able to successfully turn down the granules from the auxiliary conveyor, as the vertically moving granules make impact with the moving asphalt coated sheet, a significant portion of the granules bounces on the sheet, landing downstream and thereby causing fuzzy blend drop edges rather than sharply defined leading and trailing edges for the blend drop. This problem is magnified when the asphalt coated sheet is operated at high speeds.
U.S. Pat. No. 5,814,369 to Bockh et al. discloses another blend drop granule applicator having an applicator roll positioned to rotate directly above a moving asphalt coated sheet. The Bockh et al. reference is hereby incorporated by reference in its entirety. Granules corresponding to a desired blend drop are deposited onto the applicator roll at the top of the rotation, and when the applicator roll rotates approximately 180 degrees the blend drop falls off onto the asphalt coated sheet when the blend drop reaches the bottom of the rotation. A media retaining belt engages the applicator roll, contacting and wrapping around the applicator roll to hold the blend drop granules on the surface of the applicator roll until the applicator roll rotates about 180 degrees. At the point where the media retaining belt stops contacting or becomes disengaged from the applicator roll, the blend drop granules are released to drop onto the moving asphalt coated sheet to form the blend drop. The Bockh et al. patent states that the distance that the granules fall from the applicator roll to the asphalt coated sheet should be minimized. The Bockh et al. patent further states that the linear velocity of the applicator roll should be synchronized with that of the moving asphalt coated sheet so that the granules can be dropped precisely in the desired pattern.
There are other known procedures for depositing granules onto asphalt coated sheets. U.S. Pat. No. 2,371,605 to Carlton et al. discloses apparatus for applying grit particles or granules onto an adhesive coated sheet to make a particle coated sheet, such as a shingle. The particulate material that is falling to the coated sheet is subjected to an electromagnetic field to axially align the air-borne particles with respect to the adhesive coated sheet so that the particles will have a preferred orientation on the sheet. The preferred electrodes for affecting the air-borne particles are disc electrodes. U.S. Pat. No. 2,370,636 to Carlton discloses apparatus for coating substrates with particulate grit material by using a magnet (either an electromagnet or a permanent magnet) for attracting the particulate material to the substrate.
It would be advantageous if there could be developed a shingle blend drop technique that enables blend drops to be accurately placed on a moving asphalt coated sheet with sharply defined edge definition at high operating speeds.
The above objects as well as other objects not specifically enumerated are achieved by a method of applying blend drop granules to an asphalt coated sheet, including moving an asphalt coated sheet in a machine direction, and depositing blend drops of granules on a blend drop conveyor that is positioned above the asphalt coated sheet. The blend drop conveyor has an upper flight moving in a direction opposite the machine direction and a lower flight moving in the machine direction. The blend drops are moved from the upper flight to the lower flight of the blend drop conveyor while retaining the blend drops in contact with the blend drop conveyor by magnetic force. Finally. The blend drops are released from the blend drop conveyor for contact with the asphalt coated sheet.
According to this invention, there is also provided apparatus for applying blend drop granules to an asphalt coated sheet comprising a blend drop conveyor for receiving blend drop granules, where the blend drop conveyor is positioned above an asphalt coated sheet traveling in a machine direction. The blend drop conveyor has an upper flight moving in a direction opposite the machine direction and a lower flight moving in the machine direction. A magnet is provided for retaining the blend drops in contact with the blend drop conveyor by magnetic force while the blend drops are moved from the upper flight to the lower flight of the blend drop conveyor, and for releasing the blend drops onto the asphalt coated sheet.
According to this invention, there is also provided a method of applying blend drop granules to an asphalt coated sheet comprising moving an asphalt coated sheet in a machine direction, generating vertically moving blend drops of granules, changing the direction of the blend drops of granules to a generally horizontal orientation in the machine direction using magnetic force, and releasing the blend drops for contact with the asphalt coated sheet.
According to this invention, there is also provided apparatus for applying blend drop granules to an asphalt coated sheet comprising a blend drop depositing apparatus for generating vertically moving blend drops of granules, where the blend drop apparatus is positioned above an asphalt coated sheet moving in a machine direction. A magnet is provided for changing the direction of the blend drops of granules to a generally horizontal orientation in the machine direction, and for releasing the blend drops onto the asphalt coated sheet.
According to this invention, there is also provided a method of applying blend drop granules to an asphalt coated sheet including moving an asphalt coated sheet in a machine direction, generating a stream of blend drop granules, and intercepting the stream of blend drop granules with an array of magnets. The array includes some magnets that are switched on to attract the blend drop granules and create a blend drop, and the array includes areas without switched on magnets that do not attract granules and from which the granules fall as a waste stream of granules. The direction of the blend drops of granules is changed to a generally horizontal orientation in the machine direction, and the blend drops are released for contact with the asphalt coated sheet. The waste stream granules is recovered.
According to this invention, there is also provided apparatus for applying blend drop granules to an asphalt coated sheet comprising a blend granule applicator for generating a stream of blend drop granules. The blend granule applicator is positioned above an asphalt coated sheet moving in a machine direction. An array of magnets, including some magnets that are switched on to attract the blend drop granules and create a blend drop, and including areas without switched on magnets that do not attract granules and from which the granules fall as a waste stream of granules, is provided. The array of magnets is mounted for movement so that the blend drops are changed from a generally vertical direction to a generally horizontal orientation in the machine direction before release of the blend drops for contact with the asphalt coated sheet.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.